Compliant human-robot interaction is an essential component for integrating robots into everyday life. Many daily activities require variable impedance, and humans desire the same functionality when interacting with robots. Impedance control allows safe interaction with uncertain environments, enhancing both utility and viability. Surface electromyography (sEMG) has been identified as a candidate for naturally controlling variable impedance. During co-contraction, surface signals detected by sEMG correlate with the stiffness of corresponding joints. This correlation may be used in myoelectric impedance controllers. A neural network was trained to map the intensity of flexor and extensor forearm sEMG to the stiffness value of a prosthetic hand as it opened and closed, which in turn may be used to grip uncertain objects with the appropriate force. A similar impedance control, tele-impedance, may be applied to control a prosthetic hand aimed at generalizing grasping capabilities using kinematic synergies. The sEMG of quadriceps and hamstring muscles may be mapped to control stiffness and set-point angle for joint impedance of a prosthetic knee. There is thus a natural connection between sEMG and compliant controllers, with the controller designed to vary uniform stiffness of a prosthetic device based on sEMG.
Studies in neurophysiology indicate that humans not only control the intensity of their joint stiffness, but also the direction. While interacting in unstable environments, humans adapt their muscle activity to stabilize motion relative to the direction of instability. This suggests that multi-directional impedance control would provide a more natural extension to, and enhance capabilities of, human-robot interfaces. However, due to transient changes in sEMG, conventional myoelectric interfaces have struggled to provide reliable simultaneous control of motion, thereby deterring EMG-based impedance controllers from extending beyond a single degree-of-freedom (DOF).
Corresponding reference characters indicate corresponding elements among the view of the drawings. The headings used in the figures do not limit the scope of the claims.